In recent years, light emitting diodes (hereinafter referred to as LEDs) attract attention as a next-generation light source for lighting apparatuses. There is a demand for developing energy-saving lighting apparatuses using LEDs, since LEDs have a higher efficiency and a longer lifetime than incandescent and halogen lamps. In particular, with their small size, LEDs are expected to realize small-sized lighting apparatuses.
To use LEDs for lighting apparatuses, a plurality of LED bare chips (hereinafter referred to as LED devices) are mounted on a substrate, thereby forming an LED module, for example.
Here, a reflecting board is provided so as to surround each of the LED devices to improve light extraction efficiency of such an LED module. The reflecting board can collect light from the LED devices. Such a reflecting board can be provided as follows, for example. According to Japanese patent application publication No. 2003-124528 (patent document 1), LED devices are mounted on a substrate, and a reflecting board made of aluminum, a resin or the like is then adhered to the substrate. Here, a phosphor formed by phosphor powders and a resin may be provided so as to enclose each LED device therein, before the reflecting board is adhered.
Furthermore, Japanese patent application publication No. H11-163412 (patent document 2) discloses a technique of forming depressions in a substrate, so that part of the substrate functions as a reflecting board.
An LED module according to the patent document 1 has the following drawback. An adhesive layer adhering the substrate and the reflecting board absorbs light emitted toward the adhesive layer, out of light emitted by the LED device. In the worst case, the adhesive layer absorbs around 10% of the entire amount of light. This significantly lowers light extraction efficiency.
An LED module according to the patent document 2 does not have such a drawback that an adhesive layer absorbs light, since the substrate has a reflecting surface formed therein. However, this LED module has a problem of high cost. In detail, a wiring pattern needs to be formed on an uneven surface, due to the reflecting surface formed in the substrate. This can not be done by a common patterning method.